The stress of major surgical procedures and nutritional deprivation lead to atrophic changes in gut epithelium which significantly affect the outcome of surgical patients. In contrast, hyperplastic growth of intestinal epithelium results in colorectal neoplasm. Cyclooxygenase (COX) enzymes catalyze a key step in the conversion of arachidonic acid to prostaglandins (PGs) which play important roles in modulation of cell proliferation and cell death. Nonsteroidal antiinflammatory drugs (NSAIDs), inhibitors of COX enzymes, suppress growth of transformed intestinal epithelial cells, whereas PGs stimulate intestinal epithelial cell proliferation. The mechanism by which PGs promote intestinal epithelial growth and transformation is poorly understood. Our preliminary studies show that PGE2 induces expression of amphiregulin, an EGF family member, and transactivates receptor tyrosine kinase (RTK)-dependent signaling pathways, including the Ras and the phosphatidylinositol 3-kinase (PI3K) pathways which are essential for intestinal epithelial cell proliferation and transformation. Specific Aim 1 of this application will use an improved 3-dimensional cell growth model to elucidate the mechanisms by which PGE2 and celecoxib regulate intestinal epithelial cell growth. Functional roles of PGE2 and celecoxib in surgical animal models, including fasting/refeeding and small bowel resection, will be assessed. These experiments will delineate the basic mechanism by which PGs regulate intestinal epithelial proliferation. Specific Aim 2 will study the signaling mechanisms governing PGE2 trophic action in intestinal epithelial cells. Our focus will be the induction of EGF receptor ligands and transactivation of the PI3K signaling pathway by COX-2/PGE2. In Specific Aim 3, we will investigate the involvement of COX-2/PGs in Ras-mediated transformation of intestinal epithelial cells. Novel in vitro and in vivo models will be employed to address this question. The long-term goal of this proposal is to provide a complete assessment of molecular mechanisms mediating the trophic action of PGs and the chemopreventive effect of NSAIDs on intestinal epithelial transformation. Our results will provide a novel molecular basis for the development of more effective therapeutic strategies in the regulation of intestinal epithelial growth and transformation.